CAD implementation of design rules for aluminium extrusion dies

Aluminium extrusion is an industrial forming process that is used to produce long profiles of a constant cross-section. This cross-section is shaped by the opening in a steel tool known as the die. The understanding of the mechanics of the aluminium extrusion process is still limited. The flow of aluminium within the die is governed by tribomechanical and rate- and temperature-dependent effects that have not yet been fully mathematically modelled. As a result, it is difficult to design the die geometry in such a way that the aluminium profile complies with high customer demands regarding dimensional accuracy and surface quality. Die design has to a large extent been empirically based. This, along with a low level of automation, causes a large variation in the performance of dies. This often necessitates corrections to the die and results in a high percentage of scrap production. This dissertation is a continuation of a research project that has existed since 1991. In cooperation with the aluminium extrusion company Boalgroup, researchers at the University of Twente have worked to gain more insight into the extrusion process. With the help of finite element simulations this has led to the formulation of design rules and approaches that are based on a more fundamental understanding of the process than the existing empirical knowledge. A design method was devised that balances the exit velocity of flat dies by using a combination of variable sink-in and bearing geometry. This leads to die designs that exhibit a more stable and predictable flow balancing behaviour than traditional designs based on length variations of parallel bearings alone. In addition, a formula is given that estimates the pressure acting on the die, so that the calculation time of finite element analysis of the die deflection is drastically reduced. Along with making a contribution to the developments mentioned above, the work presented in this thesis focuses on the implementation of these design rules and approaches into CAD tools. The provided automation of these design tasks significantly accelerates the design process and increases the consistency of the results, without removing the control of the human designer. By taking constraints of the manufacturing process into account while generating the geometry, the risk that the die manufacturer has to make unexpected changes to the die design is reduced. The reduction of design time that was achieved has enabled Boalgroup to greatly increase the number of in-house die designs. Since the majority of these new designs is showing a significant performance increase, the company’s overall productivity has increased steadily, helping them to deal with the ever rising labour and energy costs.